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Pastures cover, in Brazil, around 165 million ha, most of them are at some degradation level. Recovering these pastures is essential. The objective of this study was to evaluate the sensibility of soil organic matter (SOM) and its physical attributes in pasture soil at different degradation levels (1 to 4), Capoeiras (1 and 2) and secondary Forest (Control). Samples were collected at four depths (0.00-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.40 m). We verified higher values for SOM and hydraulic conductivity (Ko) in Forest, especially in the most superficial layer (0.00-0.05). We noted low values for macroporosity in this area. In all areas under Pastures lower values for Ko were observed in the superficial layer (0.00-0.05 m) when compared to layers 0.05-0.10 and 0.10-0.20 m, which indicates that the pasture management and cattle trampling negatively affect the physical quality of the pastures. For field capacity and wilting point the average values were observed in Pasture 4 (more degraded), which caused higher values for water availability. According to the principal components analysis, except for SOM at 0.20-0.40 m, all variables studied presented correlation above 0.6. From grouping analysis, we separated 3 groups: Forest; Capoeiras 1 and Capoeira 2 and Pastures 1 to 4.

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Agriculture, forestry and other land uses are currently the second highest source of anthropogenic greenhouse gases (GHGs) emissions. In soil, these gases derive from microbial activity, during carbon (C) and nitrogen (N) cycling. To investigate how Eucalyptus land use and growth period impact the microbial community, GHG fluxes and inorganic N levels, and if there is a link among these variables, we monitored three adjacent areas for 9 months: a recently planted Eucalyptus area, fully developed Eucalyptus forest (final of rotation) and native forest. We assessed the microbial community using 16S rRNA gene sequencing and qPCR of key genes involved in C and N cycles. No considerable differences in GHG flux were evident among the areas, but logging considerably increased inorganic N levels. Eucalyptus areas displayed richer and more diverse communities, with selection for specific groups. Land use influenced communities more extensively than the time of sampling or growth phase, although all were significant modulators. Several microbial groups and genes shifted temporally, and inorganic N levels shaped several of these changes. No correlations among microbial groups or genes and GHG were found, suggesting no link among these variables in this short-rotation Eucalyptus study.

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The original version of this article unfortunately contained mistakes in the first author's name and the running page headers.

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Eucalyptus plantations offer a cost-effective and renewable source of raw material. There is substantial interest in improving forestry production, especially through sustainable strategies such as the use of plant growth-promoting bacteria. However, little is known about Eucalyptus microbiology. In this study, the endophytic bacterial community was assessed in Eucalyptus urograndis roots using culture-dependent and culture-independent techniques with plants grown under different conditions. Three phyla accounted for approximately 95% of the community, with Actinobacteria corresponding to approximately 59%. This contrasts with previous studies in which Actinobacteria accounted for only 5 to 10%. Our data also revealed a high diversity of bacteria, with 359 different genera but a high level of dominance. Six genera, Mycobacterium, Bradyrhizobium, Streptomyces, Bacillus, Actinospica, and Burkholderia, accounted for more than 50% of the classified sequences. We observed a significant influence of the treatments on some genera, causing changes in the bacterial community structure. The obtained data also suggest that Eucalyptus may benefit from biological nitrogen fixation, with many abundant genera being closely related to nitrogen-fixing bacteria. Using N-depleted media, we also cultured 95 bacterial isolates, of which 24 tested positive for the nifH gene and were able to maintain growth without any N source in the medium.

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Dark septate endophytic (DSE) fungi are facultative biotrophs that associate with hundreds of plant species, contributing to their growth. These fungi may therefore aid in the search for sustainable agricultural practices. However, several ecological functions of DSE fungi need further clarification. The present study investigated the effects of DSE fungi inoculation on nutrient recovery efficiency, nutrient accumulation, and growth of tomato plants fertilized with organic and inorganic N sources. Two experiments were carried out under greenhouse conditions in a randomized blocks design, with five replicates of tomato seedlings grown in pots filled with non-sterile sandy soil. Tomato seedlings (cv. Santa Clara I-5300) inoculated with DSE fungi (isolates A101, A104, and A105) and without DSE fungi (control) were transplanted to pots filled with 12 kg of soil which had previously received finely ground plant material [Canavalia ensiformis (L.)] that was shoot enriched with 0.7 atom % 15N (organic N source experiment) or ammonium sulfate-15N enriched with 1 atom % 15N (mineral N source experiment). Growth indicators, nutrient content, amount of nitrogen (N) in the plant derived from ammonium sulfate-15N or C. ensiformis-15N, and recovery efficiency of 15N, P, and K by plants were quantified 50 days after transplanting. The treatment inoculated with DSE fungi and supplied with an organic N source showed significantly higher recovery efficiency of 15N, P, and K. In addition, the 15N, N, P, K, Ca, Mg, Fe, Mn, and Zn content, plant height, leaf number, leaf area (only for the A104 inoculation), and shoot dry matter increased. In contrast, the only positive effects observed in the presence of an inorganic N source were fertilizer-K recovery efficiency, content of K, and leaf area when inoculated with the fungus A104. Inoculation with A101, A104, and A105 promoted the growth of tomato using organic N source (finely ground C. ensiformis-15N plant material).

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Abstract The sugarcane in Brazil is passing through a management transition that is leading to the abolition of pre-harvest burning. Without burning, large amounts of sugarcane trash is generated, and there is a discussion regarding the utilization of this biomass in the industry versus keeping it in the field to improve soil quality. To study the effects of the trash removal on soil quality, we established an experimental sugarcane plantation with different levels of trash over the soil (0%, 50% and 100% of the original trash deposition) and analyzed the structure of the bacterial and fungal community as the bioindicators of impacts. The soil DNA was extracted, and the microbial community was screened by denaturing gradient gel electrophoresis in two different seasons. Our results suggest that there are no effects from the different levels of trash on the soil chemistry and soil bacterial community. However, the fungal community was significantly impacted, and after twelve months, the community presented different structures among the treatments.

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The sugarcane in Brazil is passing through a management transition that is leading to the abolition of pre-harvest burning. Without burning, large amounts of sugarcane trash is generated, and there is a discussion regarding the utilization of this biomass in the industry versus keeping it in the field to improve soil quality. To study the effects of the trash removal on soil quality, we established an experimental sugarcane plantation with different levels of trash over the soil (0%, 50% and 100% of the original trash deposition) and analyzed the structure of the bacterial and fungal community as the bioindicators of impacts. The soil DNA was extracted, and the microbial community was screened by denaturing gradient gel electrophoresis in two different seasons. Our results suggest that there are no effects from the different levels of trash on the soil chemistry and soil bacterial community. However, the fungal community was significantly impacted, and after twelve months, the community presented different structures among the treatments.(AU)

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The sugarcane in Brazil is passing through a management transition that is leading to the abolition of pre-harvest burning. Without burning, large amounts of sugarcane trash is generated, and there is a discussion regarding the utilization of this biomass in the industry versus keeping it in the field to improve soil quality. To study the effects of the trash removal on soil quality, we established an experimental sugarcane plantation with different levels of trash over the soil (0%, 50% and 100% of the original trash deposition) and analyzed the structure of the bacterial and fungal community as the bioindicators of impacts. The soil DNA was extracted, and the microbial community was screened by denaturing gradient gel electrophoresis in two different seasons. Our results suggest that there are no effects from the different levels of trash on the soil chemistry and soil bacterial community. However, the fungal community was significantly impacted, and after twelve months, the community presented different structures among the treatments.

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O objetivo do estudo foi avaliar os efeitos de plantios de Acacia mangium, localizados no cerrado em Roraima, sobre o carbono orgânico e biomassa microbiana do solo. Foram realizadas amostragens de solo nas profundidades de 0-20 cm e 20-40 cm em dois plantios de A. mangium com cerca de cinco anos de idade, e em duas áreas de Cerrado nativo consideradas referência. Um dos plantios de A. mangium (localizado na Fazenda Cigolina) correspondeu a um plantio homogêneo (espaçamento de 3,6 m entre linhas e 2,0 m entre plantas) enquanto que o outro (localizado no Campo Experimental Água Boa - CEAB) correspondeu a um plantio em faixas com duas linhas de plantio (espaçamento de 6 m entre linhas, 2,5 m entre plantas e cerca de 30 m entre faixas). As amostras de solo foram analisadas quanto ao carbono orgânico, carbono da biomassa microbiana, respiração basal do solo e quociente metabólico, além de atributos químicos de fertilidade. Foi verificado que os plantios de A. mangium não proporcionaram aumentos significativos do carbono orgânico do solo em comparação às áreas de referência. Entretanto, na média geral, esses plantios proporcionaram aumento do carbono da biomassa microbiana do solo e redução do quociente metabólico, indicando a possibilidade de acúmulo de carbono orgânico no solo em longo prazo. Também foi observado que, em comparação ao plantio da fazenda Cigolina e às áreas de referência, o carbono microbiano do solo foi maior e acompanhado de menor quociente metabólico no plantio de A. mangium no CEAB, mostrando que a estrutura de plantio exerceu influência sobre a biomassa microbiana do solo.

The aim of this study was to evaluate the effects of Acacia mangium plantation in the Roraima's Savanna, on soil organic carbon and soil microbial biomass. Soil samplings were collected on the depths of 0-20 cm and 20-40 cm in two Acacia mangium plantation sites, about five years old, and in two sites of native savanna as reference. One of the A. mangium sites (located at Fazenda Cigolina) was composed by a homogeneous plantation (3.6 m between row and 2.0 m between trees) and, the other one (located at Campo Experimental Agua Boa Experimental - CEAB) was composed by a plantation on which the planting distances had strips of two rows 6 meters apart, 2.5 meters between trees and 30 meters between strips). Soil samples were analyzed regarding soil organic carbon, microbial biomass carbon, soil basal respiration and metabolic quotient, besides soil fertility attributes. Results showed that A. mangium plantations did not provide significant increases of organic carbon on the soil comparing with sites used as reference. However, generally, A. mangium plantation increased soil microbial biomass carbon and reduced metabolic quotient, indicating a possibility of soil organic carbon accumulation in long-term. It was also observed that, soil biomass microbial carbon was higher, followed by smaller metabolic quotient at CEAB A. mangium plantation compared with Cigolina and reference sites, showing that planting design exercised influence on soil microbial biomass.

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